The mysterious disappearance of chief engineer Jonathan Finch interrupts the construction of a trunk railway. The head of the company sends film footage with records of an accident to his friend, ex-army officer Richard Stone. Richard's is the first to notice the stone monument, and its origin becomes a perplexing riddle for him to solve. Having agreed to participate in the investigation, Richard doesn't suspect yet that he takes the dangerous path of a defender of an ancient civilization.